Antiperspirant salts, such as aluminum chlorohydrex (also called aluminum chlorohydrex polymeric salts and abbreviated here as "ACH") and aluminum zirconium glycine salts (abbreviated here as "ZAG", "ZAG complexes" or "AZG"), are known to contain a variety of polymeric and oligomeric species with molecular weights (MW) ranging from 100-500,000. It has been clinically shown that, in general, the smaller the species, the higher the efficacy on sweat reduction. A number of efforts have focused on (1) how to select the components of ACH and ZAG which affect the performance of these materials as antiperspirants and deodorants and (2) how to manipulate these components to obtain and maintain the presence of smaller types of these components.
These attempts have included the development of analytical techniques. Size exclusion chromatography ("SEC") or gel permeation chromatography ("GPC") are methods frequently used for obtaining information on polymer distribution in antiperspirant salt solutions. With appropriate chromatographic columns, at least five distinctive groups of polymer species can be detected in a ZAG, appearing in a chromatogram as peaks 1, 2, 3, 4 and a peak known as "5,6". Peak 1 is the larger Zr species (greater than 120-125 .ANG.). Peaks 2 and 3 are larger aluminum species. Peak 4 is smaller aluminum species (aluminum oligomers) and has been correlated with enhanced efficacy for both ACH and ZAG salts. Peak 5,6 is the smallest aluminum species. The relative retention time ("Kd") for each of these peaks varies depending on the experimental conditions.
Various analytical approaches for characterizing the peaks of ACH and various types of ZAG actives are found in "Antiperspirant Actives-Enhanced Efficacy Aluminum-Zirconium-Glycine (AZG) Salts" by Dr. Allan H. Rosenberg (Cosmetics and Toiletries Worldwide, Fondots, D. C. ed., Hartfordshire, UK: Aston Publishing Group, 1993, pages 252, 254-256). Using GPC, Rosenberg describes four peaks identified as A1Kd 0.0; 0.24; 0.40; and 0.60. Activated ACH is identified as material having an enriched A1Kd0.4 content. Rosenberg points out that activated AZG salts with enriched A1Kd0.4 content do not necessarily give enhanced performance in antiperspirant use and notes that zirconium polymer distributions are more important than A1Kd0.4 enrichment in predicting clinical efficacy, with lower molecular weight zirconium polymer distributions being more desirable.
Attempts to obtain antiperspirant salts with improved efficacy have included developing processes for obtaining better types of ACH such as by heating solutions of ACH with or without elevated pressure in order to depolymerize larger species into peak-4 species. Examples can be found in U.S. Pat. No. 4,359,456 to Gosling et al. Since ACH solutions may be used as starting materials for aluminum zirconium glycine (ZAG or AZG) salts, heating ACH solutions has also been used to enrich peak-4 oligomers before spray drying. Such an approach does not, however, directly address the issue of zirconium species.
U.S. Pat. No. 4,775,528 to Callaghan et al describes the formation of a solid antiperspirant composition having an Al:Zr atomic ratio from 6:1 to 1:1; the GPC profile of the antiperspirant in solution gave a ratio of at least 2:1 for peak 4/peak 3. This reference specifies that the zirconyl hydrochloride be mixed with the aluminum chlorhydroxide solution before the drying step is completed. The emphasis is placed on optimizing the aluminum chemistry and there is no discussion of any effects on the zirconium chemistry.
There have been some previous attempts at using glycine in antiperspirant salts. For example, European patent Application 0 499 456 A2 assigned to Bristol-Myers Squibb Company describes a ZAG complex and a process for making the complex comprising mixing zirconium hydroxychloride, a selected aluminum chloro species and an amino acid in aqueous solution and, optionally drying the aqueous solution to obtain a dry ZAG salt.
U.S. Pat. No. 4,435,382 to Shin et al teaches the complexing of aluminum/zirconium salts with glycine to alter the solubility of such salts in an anhydrous alcoholic vehicle to render the salts less soluble and more readily suspended therein.
U.S. Pat. No. 5,518,714 to Park discloses antiperspirants particularly suitable for roll-on products wherein the dissolution of the antiperspirant active in anhydrous ethanol or isopropanol can be inhibited by including a compound selected from those having a basic nitrogen function (such a glycine).
U.S. Pat. No. 4,871,525 to Giovanniello et al describes an aluminum zirconium hydroxyl halide glycinate complex having improved antiperspirant activity wherein the glycine is used to prevent gel formation. The ratio of Zr to glycine is less than 1:1 (see column 5, lines 36-39).
U.S. Pat. No. 5,225,187 to Carmody teaches a process for preparing concentrated aluminum/zirconium/glycine solutions which can produce a solution having 45-50% solids. The ratio of Zr to glycine is in the range of 0.8-1-1.2:1 (see column 3, lines 64-66).
U.S. Pat. No. 5,589,196 to Callaghan et al discloses an antiperspirant composition including zirconyl hydroxy chloride and aluminum chlorhydroxide which can contain a neutral amino acid such as glycine in an amount of 1:1 glycine to zirconyl hydroxy chloride.
U.S. Pat. No. 5,643,558 to Provancal et al teaches a process for preparing an enhanced efficacy aluminum/zirconium antiperspirant salt in a polyhydric alcohol in which an alkaline glycinate salt may be added to the polyhydric alcohol prior to the addition of the salt to raise the pH of the recovered product. This zinc glycinate is in addition to any glycine present in the Al/Zr salt.
European Patent Application 0 047 650 A2 assigned to the Procter & Gamble Company discloses an antiperspirant composition obtained by forming a water-soluble, stable complex including a combination of an aluminum compound, a zirconium compound, a neutral amino acid and an inorganic acidic compound. The amino acid is present in a minor proportion.
European Patent Application EP 0 653 203 A1 to Rosenberg et al describes a process for making ZAG salt with high antiperspirant activity. According to this reference, glycine is added to Zr starting materials at ambient temperature, and the mixed Zr/glycine is admixed with the aluminum chlorohydrate starting material immediately prior to spray drying in a continuous or semi-continuous operation.
Spray drying AZG within a prescribed time frame to fix the desired distributions of the 4 peaks in a powder has also been suggested. See Rosenberg, A., "New Antiperspirant Salt Technology" (Cosmetics and Toiletries Worldwide, Fondots, D. C. ed., Hartfordshire, UK: Aston Publishing Group, 1993, pages 214-218).
Previous processes for making active salts generally include a method described by the following Reaction Scheme I: EQU ZrOCl or ZrOHCl+glycine+water.fwdarw.Solution A EQU Solution A+Al(OH).sub.5 Cl+water.fwdarw.Solution B
The glycine is used in an amount up to a Zr/glycine ratio of 1:1. Solution B is then immediately spray dried to obtain the final powder form of the active salt. Such processes may produce ZAG salts with more small Zr polymer species in powder form; however, stabilizing small Zr polymer species, in high concentration aqueous solutions (above 10% weight/weight) (for example, in the range of 10-50% by weight based on the total weight of the solution) over prolonged periods of time, still remains a challenge.
Thus, it is an object of the invention to stabilize small zirconium species in an aqueous solution of ZAG wherein the aqueous solution of these salts will have a reduced formation of higher molecular weight zirconium species. It is a further object to provide aluminum zirconium glycine solutions which have enhanced stability by the use of an amino acid such as glycine in an amount which is greater than 1:1 Zr: amino acid. It is another object of the invention to provide aluminum zirconium glycine solution which can be formulated into cosmetic products having improved efficacy and increased shelf-life. It is another object of the invention to provide a process for producing aluminum zirconium-glycine solutions which have improved efficacy in antiperspirant and/or deodorant compositions and which do not require an immediate spray drying step. It is still a further object of the invention to provide an improved method for characterizing the zirconium species present in aqueous solutions, especially aqueous solutions of ZAG. These and other objects of the invention will be apparent from the following description.